Photocatalytically Induced Degradation of Nano-TiO2-Modified Paint Coatings Under Low-Radiation Conditions

Photocatalytic coatings incorporating nano-TiO2 have emerged as effective solutions for air purification, utilizing solar radiation to degrade airborne pollutants. However, the long-term stability of such coatings, particularly those based on organic binders, remains a concern due to their susceptibility to photocatalytic-driven degradation. This study investigates the effects of low-intensity UV-A irradiation (1–10 W/m2) on acrylic-based photocatalytic coatings’ structural integrity and air purification performance. The findings reveal that significant binder decomposition occurs even under low irradiation conditions—comparable to natural sunlight exposure in Northern and Central Europe during autumn and winter. The surface porosity increased from 2.28% to 9.09% due to polymer degradation, exposing more nano-TiO2 particles and enhancing NO removal efficiency from approximately 120 µg/hm2 to 360 µg/hm2 under UV-A irradiation (1 W/m2). However, this process also resulted in benzene emissions reaching approximately five ppb, raising concerns about secondary pollution and the potential release of nano-TiO2 due to polymer matrix disintegration. These findings highlight the need for optimized coating formulations that balance photocatalytic efficiency with long-term material stability, mitigating the environmental and health risks associated with secondary pollutant emissions.